<style>
* {
  box-sizing: border-box;
}
.wrapper {
  display: flex;
}
.wrapper > div {
  border-radius: 5px;
  background-color: rgb(207, 232, 220);
  padding: 1em;
  flex: 1;
}
</style>
<div class="wrapper">
  <div class="box1">One</div>
  <div class="box2">Two</div>
  <div class="box3">Three</div>
</div>